To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
Research into a multi-carrier system using a non-orthogonal waveform to increase frequency confinement while transmitting data at a high speed has been actively conducted in recent years. As the representative multi-carrier system using the non-orthogonal waveform, there is a filter bank multi-carrier (hereinafter, FBMC) system using offset-QAM. Further, the FBMC system supporting general QAM instead of the offset-QAM has also been proposed. Further, generalized frequency division multiplexing (GFDM) that has been actively researched in recent years also belongs to a multi-carrier system using a non-orthogonal wave.
In the orthogonal frequency division multiplexing (OFDM) system, data are allocated to each subcarrier and are converted into a time domain signal by an inverse FFT (IFFT) calculation and transmitted. In this case, each data may be considered to be modulated by a rectangular filter and may keep orthogonality between the respective subcarriers due to the rectangular filter. However, when the rectangular filter is applied, emission power of a considerable magnitude (−13 dB) is generated, and therefore in the case of the OFDM, a considerable guard band is required, such that maximum frequency efficiency is not obtained. Alternatively, the multi-carrier system using the non-orthogonal waveform uses a filter having a time impulse response having a length longer than that of the rectangular filter in OFDM to generate much smaller emission power, and as a result, requires a smaller guard band, thereby increasing frequency use efficiency.
In the multi-carrier system using the non-orthogonal waveform, a data symbol also has a symbol having a length longer than that of the OFDM due to the long impulse response filter. The non-orthogonal system adopts an overlap & sum structure to prevent the frequency efficiency from being reduced due to an extended symbol length.